The invention relates to an electro-acoustical measuring device for testing the chronological resolution of hearing by means of acoustic signals to be supplied to the ear under examination via an earpiece, said acoustic signals consisting of a continuous test tone which can be interrupted and masking sound which can be pulse-modulated and whose pitch and level can be separately adjusted. A device of this type is known, for example, from "ACUSTICA", Vol. 36 (1976/77), Pages 113 through 120, particularly FIG. 1.
In addition to the frequency resolution of hearing which can be determined in a simple manner with audiometers, its chronological resolution in the acceptance of information, particularly in that of speech, also plays a very important role. If, after loud vowels, the hearing does not become sensitive quickly enough that it can also perceive following, soft consonants, the speech is not understood. This effect is also noticeable given persons with normal hearing when a speaker speaks quickly in a very reverberant space (for example, announcements at railroad stations which are often completely incomprehensible). The soft consonants which, however, are very important for the information contained in speech are then covered by the reverberant, loud vowels.
The chronological resolution of hearing can be described by means of simultaneous, pre- and post-masking. The combination proceeding from the effects of these maskings is measured in the so-called listening threshold period patterns of periodically amplitude-modulated maskers, as is treated in the reference cited in the above introductory paragraph. Thereby, a rectangular modulation is periodically undertaken with a modulation frequency of, for example, 15.6 Hz. The period of this masking sound then amounts to 64 ms (32 ms on and 32 ms off). A short test tone pulse, for example 4 ms long, is respectively offered within this period at a specific point in time (variable from measuring point to measuring point). Since the periods repeat with 15.6 Hz, the test sound is a pulse sequence of acoustical pulses of the repetition rate of 15.6 Hz. Masking sound and test sound are chronologically synchronized: in order to identify the listening threshold period pattern, the listening threshold of the test sound is measured as a function of the chronological shift of the test sound within one period of the masking sound.
The result of such a measurement upon employment of a device according to the present invention is illustrated in FIG. 1 for a masking octave noise of the mean frequency 1.5 kHz (completely rectangularly modulated with 15.6 Hz in its amplitude). The test tone frequency amounts to 1.5 kHz; the test tone duration amounts to 4 ms given 2 ms rise and decay time. The level L.sub.T, from which the barely perceptible test tone pulse L.sub.T was excerpted, is illustrated as a function of the delay time t.sub.v within a period of the masking sound. In order to be able to identify the investigated interrelationship with sufficient precision, sixteen measuring points within the period of 32 ms were selected. In FIG. 1, a period of the masking sound 1, 1a (oblique shading) as well as a test pulse 2 (vertical shading) are illustrated below the abscissa. The level L.sub.M of the octave noise, from which the masking sound 1, 1a was excerpted, amounts to 50 dB. The listening threshold period pattern reveals high listening thresholds in those parts of the period in which the masking sound is switched on. After the masking sound 1 is switched off, the listening threshold sinks more slowly (post-masking), then it increases again before the masking noise 1a is again switched on (pre-masking). The quiescent hearing threshold (RHS), which is indicated by means of an arrow 3 at the ordinate, is not reached during the pause lying between 1 and 1a. On the contrary, the minimum of the listening threshold period pattern, given the parameters selected, lies somewhat below the mean between the maximum and the quiescent hearing threshold (RHS).